Historically, vice presidents have been runners-up to the president, serving as necessary political figures who stood in for the president in cases of emergency or death. Today, they often serve as a counterbalance to a president’s weaknesses and a complement to his strengths. The surprise nomination of Gov. Sarah Palin of Alaska by Ariz. Sen. John McCain speaks to the increasingly prominent role vice presidential nominees have in the lead-up to an election. But what happens once they arrive at the White House?

Vice President Dick Cheney has had a very prominent political role, a continuation of a tradition that many see as started by President Carter and his vice president, Walter Mondale. Huffington Post blogger Andy Rosenberg wrote earlier in September that—as is the tradition in recent decades—Cheney has filled in for Bush in areas in which the president is inexperienced or, as Rosenberg puts it, “absent.”

For Sen. Biden and Gov. Palin, the vice presidential role would mean starkly different things, reflecting the candidates’ different experiences—Biden’s as a three-decade senator and head of the Senate Committee on Foreign Relations; and Palin’s as the mayor of Wasilla, Alaska, and then the governor of the state. There is no doubt that the tradition begun by Carter and accelerated by Cheney will see either candidate having an important and far from symbolic role in the White House.

Prior to the announcement of Sens. Obama and McCain’s vice presidential picks, Michael Barone observed in RealClearPolitics that “vice presidents in the last five administrations have been important officers of government. (Yes, including Dan Quayle … ).” Explaining the evolving role of the vice president from the first U.S. election to the present day, Barone says, “The framers of the Constitution created the vice presidency to solve the problem of succession. They expected that electors meeting in state capitals would vote for two candidates from different states, with the No. 2 vote-getter becoming vice president. It worked well twice. Then the unexpected emergence of political parties produced bizarre results.”

When a tie occurred in 1800 between Thomas Jefferson and Aaron Burr, the Twelfth Amendment passed, indicating that electors must vote separately for the vice president and president. This, Barone says, led to “the nomination of mediocrities to balance a ticket geographically or ideologically.” It was President Carter and his second-in-command, Walter Mondale, who set the precedent for the current practice. “Mondale had offices and staffers in the West Wing, regular one-on-one meetings with the president and access to top appointees. Their example has been followed since.”

In 1988, President George H.W. Bush’s vice president, then-Sen. Dan Quayle, achieved the lowest approval rating of any vice presidential nominee in modern times. In an October 1988 op-ed in the New York Times, Anthony Lewis noted, “Even among supporters of George Bush, 32 percent said they would worry” if Sen. Quayle became president. But the candidates received a surge after the Republican National Convention and a stiff campaign against Democratic nominee Michael Dukakis spurred Bush and Quayle to victory in spite of this early uncertainty about Bush’s VP choice.

Quayle did suffer a low approval rating during Bush’s first term, and in 1992 there was some speculation in the lead-up to Bush’s potential second term that he might drop Quayle. Political science professor Robert O’Connor dismissed that idea, noting at the time that “vice presidential candidates have never had much effect on presidential elections… Quayle had the largest effect of any recent vice presidential candidate [and] he only lost about one percentage point for Bush in 1988.”

After September 11, Vice President Dick Cheney was seen to have taken the reins on a global operation against terrorists. The subject was explored in the PBS Frontline documentary “The Dark Side” (2006). According to PBS, Cheney “seized the initiative and pushed for expanding presidential power, transforming America’s intelligence agencies and bringing the war on terror to Iraq.”

Andy Rosenberg of The Huffington Post argues that Vice President Cheney pushed the envelope for vice presidents. “In the wake of eight years of Dick Cheney, the old assumptions regarding the inconsequence of vice presidential candidates just don’t hold up anymore. The oft-repeated fact that Dan Quayle was on a winning ticket makes a point that has been rendered obsolete.” But does Cheney’s role mean that every vice president will have such responsibilities?

Cheney helped bolster the Bush ticket with his foreign policy experience. Two weeks ago, Sen. Chuck Hagel, a Republican from Nebraska, commented in an interview that Gov. Palin does not have “any foreign policy credentials” and a recent Wall Street Journal/NBC News poll reflected Sen. Quayle’s ratings in the run-up to the 1988 election: “one in three [respondents] said they were ‘not at all’ comfortable with the idea of Gov. Palin as vice president.”

But Gov. Palin has confidently defined her potential role in the White House, outlining what she would do as vice president at campaign rallies. Palin said part of her responsibility “would be to help McCain, ‘implement his “all of the above” strategy for energy independence,’” the Associated Press reported Sept. 15. She would also work on “government reform and helping families with special needs children.”

For Sen. Biden, the vice presidential role would focus on foreign policy, balancing Ill. Sen. Obama’s relative inexperience on the world stage. Steven Thomma of McClatchy Newspapers drew similarities between Sen. Biden and Vice President Cheney in August, saying that Biden “will help reassure some voters nervous about Obama’s lack of experience on foreign affairs, much as Dick Cheney did when he was chosen as the young George W. Bush’s running mate.” But many have criticized Sen. Biden for his verbal gaffes, which often embarrass him and whomever he is addressing, and many times include factual errors, which could spell trouble in a diplomatic context.